effects of botox® may spread hours to weeks after injection, causing serious symptoms. alert your doctor right away as difficulty swallowing, speaking, breathing, eye problems, or muscle weakness can be signs of a life-threatening condition. side effects may include allergic reactions, neck and injection site pain, fatigue, and headache. don't take botox® if there's a skin infection. tell your doctor your medical history, muscle or nerve conditions, and medications, including botulinum toxins, as these may increase the risk of serious side effects. for a limited time, you can qualify for two treatments at no cost. stand up to chronic migraine. talk to a headache specialist today.